U.S. patent application number 10/049788 was filed with the patent office on 2002-10-10 for glass substrate for an inorganic el display.
Invention is credited to Nagakane, Tomohiro, Yamazaki, Hiroki.
Application Number | 20020147102 10/049788 |
Document ID | / |
Family ID | 18733142 |
Filed Date | 2002-10-10 |
United States Patent
Application |
20020147102 |
Kind Code |
A1 |
Yamazaki, Hiroki ; et
al. |
October 10, 2002 |
Glass substrate for an inorganic el display
Abstract
A glass substrate for an inorganic EL display comprises an
aluminosilicate glass, contains CaO, SrO, BaO, and ZrO.sub.2 the
contents of which fall within ranges of, by mass percent, 0-13%
CaO, 0-13% SrO, 0-13% BaO, 0-10% ZrO.sub.2, and 0-13%
CaO+SrO+BaO+ZrO.sub.2, and has the strain point not lower than
520.degree. C.
Inventors: |
Yamazaki, Hiroki; (Koga-gun,
JP) ; Nagakane, Tomohiro; (Moriyama-shi, Shiga,
JP) |
Correspondence
Address: |
WILLIAM COLLARD
COLLARD & ROE, P.C.
1077 NORTHERN BOULEVARD
ROSLYN
NY
11576
US
|
Family ID: |
18733142 |
Appl. No.: |
10/049788 |
Filed: |
February 15, 2002 |
PCT Filed: |
August 6, 2001 |
PCT NO: |
PCT/JP01/06738 |
Current U.S.
Class: |
501/70 ;
501/69 |
Current CPC
Class: |
C03C 3/083 20130101;
C03C 3/087 20130101; C03C 3/085 20130101 |
Class at
Publication: |
501/70 ;
501/69 |
International
Class: |
C03C 003/085; C03C
003/087 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2000 |
JP |
242061/2000 |
Claims
1. An inorganic EL display glass substrate comprising an
aluminosilicate glass, containing CaO, SrO, BaO, and ZrO.sub.2 the
contents of which fall within ranges of, by mass percent, 0-13%
CaO, 0-13% SrO, 0-13% BaO, 0-10% ZrO.sub.2, and 0-13%
CaO+SrO+BaO+ZrO.sub.2, and having the strain point not lower than
520.degree. C.
2. An inorganic EL display glass substrate as claimed in claim 1,
wherein said substrate has a coefficient of thermal expansion of
50-100.times.10.sup.-7/.degree. C. within a temperature range of
30-380.degree. C.
3. An inorganic EL display glass substrate as claimed in claim 1,
wherein the contents of CaO, SrO, BaO, and ZrO.sub.2 fall within
ranges of, by mass percent, 0-13% CaO, 0-13% SrO, 0-13% BaO, 0-10%
ZrO.sub.2, and 7-13% CaO+SrO+BaO+ZrO.sub.2.
4. An inorganic EL display glass substrate as claimed in claim 3,
wherein said substrate has a coefficient of thermal expansion of
50-100.times.10.sup.-7/.degree. C. within a temperature range of
30-380.degree. C.
5. An inorganic EL display glass substrate as claimed in claim 1,
wherein the contents of CaO, SrO, BaO, and ZrO.sub.2 fall within
ranges of, by mass percent, 0-6% CaO, 0-13% SrO, 0-13% BaO, 0-10%
ZrO.sub.2, and 7-13% CaO+SrO+BaO+ZrO.sub.2.
6. An inorganic EL display glass substrate as claimed in claim 5,
wherein said substrate has a coefficient of thermal expansion of
50-100.times.10.sup.-7/.degree. C. within a temperature range of
30-380.degree. C.
Description
FIELD OF THE ART
[0001] This invention relates to a glass substrate for an inorganic
EL (electro luminescence) display.
BACKGROUND ART
[0002] An inorganic EL (electro luminescence) display has a number
of advantages, such as a low profile, a light weight, sharpness of
a displayed image, a high-definition picture being achieved because
fine resolution of picture is easily obtained, full color images
being available, and so on. Thus, such display is likely to be more
and more spread as a display apparatus.
[0003] As illustrated in FIG. 1 for example, the inorganic EL
display has a structure comprising a rear substrate 10 on which a
metal electrode 11, a first dielectric layer 12, an inorganic EL
phosphor layer 13, a second dielectric layer 14, an ITO (indium tin
oxide) electrode 15, a RGB (red-green-blue) color filter 16, and a
front substrate 17 are successively laminated.
[0004] In the inorganic EL display having the above-mentioned
structure, the metal electrode 11 and the ITO electrode 15 are
applied with an electric voltage to excite the inorganic EL
phosphor layer 13 so that a light beam is produced. The light beam
is subjected to color conversion by the RGB color filter 16.
[0005] In recent years, it is attempted to use the inorganic EL
display in a home television. For a large-sized display, there is a
demand for a substrate having a size on the order of 40-inch to
60-inch models. In case where a small-sized display of a 12-inch or
smaller model is produced, the production efficiency is much high
if a large substrate is at first prepared and then cut and divided
into a plurality of individual substrates, rather than preparing
rear substrates one by one. In this respect also, the substrate is
desired to be large in size.
[0006] In a conventional production process of the inorganic EL
display, a dielectric layer or a phosphor layer is formed on the
rear substrate in the following manner. The material thereof is
applied on the rear substrate by a paste method or the like, dried,
and then fired at about 800.degree. C. Therefore, as the rear
substrate, use is mainly made of an alumina substrate high in heat
resistance.
[0007] However, it is very difficult to produce a large-sized
substrate from alumina so that the cost is extremely high.
Furthermore, such alumina substrate has a high density of about 4
g/cm.sup.3. This is a large obstacle to the reduction in weight of
the inorganic EL display.
[0008] Under the circumstances, it is considered to use a glass
substrate as the rear substrate. At first, consideration has been
made of a soda lime glass used as a front substrate of the
inorganic EL display. This glass substrate is characterized by a
low cost, formability into a large plate, and a low density.
However, the soda lime substrate is low in heat resistance. If it
is fired at a high temperature of 800.degree. C., thermal
deformation is caused. Therefore, this glass substrate can not be
used as the rear substrate.
[0009] In recent years, a low firing temperature is sought in order
to lower the production cost of the inorganic EL display. At
present, development is made of a technique of forming a uniform
dielectric layer or a uniform phosphor layer at a temperature on
the order of 650-700.degree. C. so that a display having a
sufficient color purity can be produced. Even under the
above-mentioned firing condition, however, thermal deformation also
occurs if the soda lime glass substrate is used as the rear
substrate.
[0010] Therefore, in case where the soda lime glass substrate is
used as the rear substrate, the dielectric layer and the phosphor
layer must be fired at a temperature not higher than 650.degree.
C., i.e., at a temperature such that the glass substrate exhibits
no thermal deformation. However, such low-temperature firing fails
to provide the uniform dielectric layer or the uniform phosphor
layer. As a consequence, the inorganic EL display is remarkably
deteriorated in color purity to become unsuitable for use.
[0011] Furthermore, the soda lime glass has a volume resistivity
(log .rho.) as low as 8.4 .OMEGA. .multidot.cm at 150.degree. C. so
that the mobility of alkali components in the glass is large. If
this glass is used as the rear substrate of the inorganic EL
display, the alkali components in the glass reacts with the metal
electrode to unfavorably change the electric resistance of the
electrode material.
[0012] It is therefore an object of this invention to provide an
inorganic EL display glass substrate which is free from thermal
deformation even if it is fired at 650-700.degree. C., which is
high in volume resistivity as compared with a soda lime glass
substrate, which can be reduced in weight and increased in size,
and which is thus suitable as a rear substrate.
[0013] Other objects of this invention will become clear as the
description proceeds.
DISCLOSURE OF THE INVENTION
[0014] As a result of various experiments repeatedly carried out
for the purpose of achieving the above-mentioned object, the
present inventors have found out that, in order to avoid thermal
deformation in a firing step at 650-700.degree. C., a glass must
have a strain point not lower than 520.degree. C., and propose this
invention.
[0015] Specifically, according to this invention, there is provided
an inorganic EL display glass substrate comprising an
aluminosilicate glass, containing CaO, SrO, BaO, and ZrO.sub.2 the
contents of which fall within ranges of, by mass percent, 0-13%
CaO, 0-13% SrO, 0-13% BaO, 0-10% ZrO.sub.2, and 0-13%
CaO+SrO+BaO+ZrO.sub.2, and having the strain point not lower than
520.degree. C.
[0016] Preferably, the inorganic EL display glass substrate has a
coefficient of thermal expansion of 50-100.times.10.sup.-7/.degree.
C. within a temperature range of 30-380.degree. C.
[0017] The inorganic EL display glass substrate according to this
invention has the strain point not lower than 520.degree. C.
(preferably not lower than 550.degree. C., more preferably not
lower than 570.degree. C.). Therefore, if it is used as a rear
substrate and fired at 650-700.degree. C., no thermal deformation
is caused. Furthermore, the aluminosilicate glass has a high volume
resistivity as compared with a soda lime glass. Therefore, an
electric resistance of an electrode material of the inorganic EL
display hardly varies.
[0018] Generally, an aluminosilicate glass substrate is
disadvantageous in that it is easily broken as compared with a soda
lime glass substrate. However, it has been found out that CaO, SrO,
BaO, and ZrO.sub.2 are components deteriorating a crack-resistant
characteristic of the glass. In view of the above, the total
content of these components is restricted to 13% or less.
Therefore, the inorganic EL display substrate according to this
invention is excellent in crack-resistant characteristic and is
hardly broken.
[0019] In this invention, it is more preferable that the
coefficient of thermal expansion of the substrate is
50-100.times.10.sup.-7/.degree. C. (preferably
60-90.times.10.sup.-7/.degree. C.) within a temperature range of
30-380.degree. C. to approximate the coefficient of thermal
expansion of a front substrate or a dielectric layer. In this
event, thermal stress is not produced between the substrate and the
front substrate or the dielectric material.
[0020] The glass substrate according to this invention can be
formed into a large plate. Therefore, a large-sized display
substrate for 40-inch to 60-inch models can be produced at a low
cost. Furthermore, it is possible to economically produce a
small-sized display substrate of a 12-inch or smaller model by
first producing a large plate glass and then cutting and dividing
the same into a plurality of individual substrates.
[0021] The glass substrate according to this invention can be
produced by a well-known sheet glass forming technique, i.e., a
float process, a roll-out process, a slot down-draw process, an
overflow down-draw process, and so on. According to these method,
it is possible to form a large-sized substrate.
[0022] Specifically, the inorganic EL display glass substrate has a
composition of 45-85% SiO.sub.2, 1-20% Al.sub.2O.sub.3, 0-15% MgO,
0-13% CaO, 0-13% SrO, 0-13% BaO, 0-2% Li.sub.2O, 0-10% Na.sub.2O,
0-20% K.sub.2O, 0-10% ZrO.sub.2, and 0-13%
CaO+SrO+BaO+ZrO.sub.2.
[0023] In the above-mentioned range, the following two compositions
are particularly preferable.
[0024] A composition of 45-85% (preferably 50-70%) SiO.sub.2, 1-20%
(preferably 1-15%) Al.sub.2O.sub.3, 0-15% (preferably 1-7%) MgO,
0-13% (preferably 1-10%) CaO, 0-13% (preferably 0-8%) SrO, 0-13%
(preferably 0-8%) BaO, 0-2% (preferably 0-1%) Li.sub.2O, 0-10%
(preferably 0-6%) Na.sub.2O, 0-20% (preferably 4-15%) K.sub.2O,
0-10% (preferably 0-7%) ZrO.sub.2, and 0-13% (preferably 8-12%)
CaO+SrO+BaO+ZrO.sub.2.
[0025] Alternatively, a composition of 45-85% (preferably 50-70%)
SiO.sub.2, 1-20% (preferably 1-15%) Al.sub.2O.sub.3, 0-15%
(preferably 1-7%) MgO, 0-6% (preferably 1-5%) CaO, 0-13%
(preferably 0-8%) SrO, 0-13% (preferably 0-8%) BaO, 0-2%
(preferably 0-1%) Li.sub.2O, 0-10% (preferably 0-6%) Na.sub.2O,
0-20% (preferably 4-15%) K.sub.2O, 0-10% (preferably 0-7%)
ZrO.sub.2, and 0-13% (preferably 6-12%) CaO+SrO+BaO+ZrO.sub.2.
[0026] The reason why the former composition of the glass is
defined as above will be described below.
[0027] SiO.sub.2 is a component elevating the strain point of the
glass. If the content of SiO.sub.2 is smaller than 45%, the strain
point of the glass is lowered so that thermal deformation tends to
occur. On the other hand, the content greater than 85% is
unfavorable because the coefficient of thermal expansion is
excessively small.
[0028] Al.sub.2O.sub.3 is also a component elevating the strain
point of the glass. If the content of Al.sub.2O.sub.3 is smaller
than 1%, the strain point of the glass is lowered so that thermal
deformation tends to occur. On the other hand, the content of
Al.sub.2O.sub.3 being greater than 20% is unfavorable because the
meltability of the glass is decreased.
[0029] MgO is a component controlling the coefficient of thermal
expansion of the glass and improving the meltability. The content
of MgO being greater than 15% is unfavorable because the glass is
readily devitrified.
[0030] CaO is a component improving the meltability and the volume
resistivity of the glass. The content of CaO being greater than 13%
is unfavorable because the glass is readily devitrified.
[0031] SrO is a component increasing the meltability and the volume
resistivity of the glass. The content of SrO being greater than 13%
is unfavorable because the density of the glass is increased so
that the weight of the substrate is excessively heavy.
[0032] Like SrO, BaO is a component increasing the meltability and
the volume resistivity of the glass. The content of BaO being
greater than 13% is unfavorable because the density of the glass is
increased so that the weight of the glass is excessively heavy.
[0033] Li.sub.2O is a component controlling the coefficient of
thermal expansion of the glass and increasing the meltability. The
content of Li.sub.2O being greater than 2% is unfavorable because
the strain point of the glass is lowered.
[0034] Like Li.sub.2O, Na.sub.2O is a component controlling the
coefficient of thermal expansion of the glass and increasing the
meltability. The content of Na.sub.2O being greater than 10% is
unfavorable because the strain point of the glass is lowered.
[0035] Like Li.sub.2O and Na.sub.2O, K.sub.2O is a component
controlling the coefficient of thermal expansion of the glass and
increasing the meltability. The content of K.sub.2O being greater
than 20% is unfavorable because the strain point of the glass is
lowered.
[0036] However, if the glass contains a large amount of Na.sub.2O
and K.sub.2O, alkali ions in the glass are diffused in the
dielectric layer or the like during firing to readily cause the
deterioration in characteristics. Therefore, the total content of
Na.sub.2O and K.sub.2O is desirably suppressed to 20% or less.
[0037] ZrO.sub.2 is a component elevating the strain point of the
glass. The content of ZrO.sub.2 being greater than 10% is
unfavorable because the density of the glass is increased so that
the weight of the substrate is increased.
[0038] The total content of CaO, SrO, BaO, and ZrO.sub.2 is limited
to 7-13%. If the total content of these components is greater than
13%, the crack-resistant characteristic of the glass is remarkably
degraded. The content of 7% or less is unfavorable because the
strain point of the glass is lowered.
[0039] The reason why the latter composition of the glass is
defined as above will be described below.
[0040] SiO.sub.2 is a component elevating the strain point of the
glass. If the content of SiO.sub.2 is smaller than 45%, the strain
point of the glass is lowered so that thermal deformation tends to
occur. On the other hand, the content greater than 85% is
unfavorable because the coefficient of thermal expansion is
excessively small.
[0041] Al.sub.2O.sub.3 is also a component elevating the strain
point of the glass. If the content of Al.sub.2O.sub.3 is smaller
than 1%, the strain point of the glass is lowered so that thermal
deformation tends to occur. On the other hand, the content of
Al.sub.2O.sub.3 being greater than 20% is unfavorable because the
meltability of the glass is decreased.
[0042] MgO is a component controlling the coefficient of thermal
expansion of the glass and improving the meltability. The content
of MgO being greater than 15% is unfavorable because the glass is
readily devitrified.
[0043] CaO is a component improving the meltability and the volume
resistivity of the glass. The content of CaO being greater than 6%
is unfavorable because the crack-resistant characteristic is
decreased.
[0044] SrO is a component increasing the meltability and the volume
resistivity of the glass. The content of SrO being greater than 13%
is unfavorable because the density of the glass is increased so
that the weight of the substrate is excessively heavy.
[0045] Like SrO, BaO is a component increasing the meltability and
the volume resistivity of the glass. The content of BaO being
greater than 13% is unfavorable because the density of the glass is
increased so that the weight of the glass is excessively heavy.
[0046] Li.sub.2O is a component controlling the coefficient of
thermal expansion of the glass and increasing the meltability. The
content of Li.sub.2O being greater than 2% is unfavorable because
the strain point of the glass is lowered.
[0047] Like Li.sub.2O, Na.sub.2O is a component controlling the
coefficient of thermal expansion of the glass and increasing the
meltability. The content of Na.sub.2O being greater than 10% is
unfavorable because the strain point of the glass is lowered.
[0048] Like Li.sub.2O and Na.sub.2O, K.sub.2O is a component
controlling the coefficient of thermal expansion of the glass and
increasing the meltability. The content of K.sub.2O being greater
than 20% is unfavorable because the strain point of the glass is
lowered.
[0049] However, if the glass contains a large amount of Na.sub.2O
and K.sub.2O, alkali ions in the glass are diffused in the
dielectric layer or the like during firing to readily cause the
deterioration in characteristics. Therefore, the total content of
Na.sub.2O and K.sub.2O is desirably suppressed to 20% or less.
[0050] ZrO.sub.2 is a component elevating the strain point of the
glass. The content of ZrO.sub.2 being greater than 10% is
unfavorable because the density of the glass is increased so that
the weight of the substrate is increased.
[0051] The total content of CaO, SrO, BaO, ZrO.sub.2 is limited to
13% or less as described above. The total content of these
components being greater than 13% is unfavorable because the
crack-resistant characteristic of the glass is remarkably
degraded.
[0052] In this invention, the following components may be added in
addition to the above-mentioned components.
[0053] In order to improve the crack-resistant characteristic of
the glass substrate, P.sub.2O.sub.5 may be added up to 10%,
preferably up to 5%. An increase in content of P.sub.2O.sub.5 tends
to decrease the volume resistivity of the glass. Therefore, the
content is desirably suppressed to 10% or less.
[0054] In order to improve the chemical durability of the glass and
to prevent coloration of the glass by ultraviolet rays, TiO.sub.2
may be added up to 5%, preferably up to 1%. An increase in content
of TiO.sub.2 tends to increase the density of the glass. Therefore,
the content is desirably suppressed to 5% or less.
[0055] In order to improve the meltability of the glass,
B.sub.2O.sub.3 may be added up to 5%, preferably up to 2%. An
increase in content of B.sub.2O.sub.3 tends to lower the strain
point of the glass. Therefore, the content is desirably suppressed
to 5% or less.
[0056] A fining agent such as As.sub.2O.sub.3, Sb.sub.2O.sub.3,
SO.sub.3, and Cl may be added up to 1% in total. A coloring agent
such as Fe.sub.2O.sub.3, CoO, NiO, Cr.sub.2O.sub.3, and CeO.sub.2
may be added up to 1% each. However, in view of the environmental
aspect, the addition of hazardous As.sub.2O.sub.3 must be
avoided.
[0057] In this invention, the density of the glass substrate is
preferably as low as possible because the inorganic EL display is
reduced in weight. Specifically, the density is desirably not
greater than 3.0 g/cm.sup.3 (preferably not greater than 2.8
g/cm.sup.3).
BRIEF DESCRIPTION OF THE DRAWING
[0058] FIG. 1 is a sectional view for describing the structure of
an inorganic EL display.
BEST MODE FOR EMBODYING THE INVENTION
[0059] Now, examples of this invention will be described in
detail.
[0060] Table 1 and 2 show examples (samples Nos. 1-10) of an
inorganic EL display glass substrate of this invention and
comparative examples (samples Nos. 11 and 12).
[0061] The sample No. 12 as the comparative example is a soda lime
glass substrate commercially available as a window panel glass for
a building.
1 TABLE 1 Examples No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 Composition
(mass %) SiO.sub.2 63.7 63.8 67.8 67.5 63.8 62.6 Al.sub.2O.sub.3
6.0 7.9 7.9 2.8 7.9 10.0 MgO 3.6 3.6 3.6 4.5 3.6 6.2 CaO 2.5 2.5
5.5 6.0 2.5 1.0 SrO 7.5 6.5 3.5 -- -- 6.5 BaO -- -- -- 3.1 6.5 --
Li.sub.2O -- -- 0.4 -- -- -- Na.sub.2O 2.5 2.5 2.5 4.9 2.5 5.0
K.sub.2O 12.5 12.5 7.1 7.9 12.5 8.0 ZrO.sub.2 0.5 0.5 0.5 2.1 0.5
0.5 TiO.sub.2 -- -- -- -- -- -- P.sub.2O.sub.5 1.0 -- 1.0 1.0 -- --
SO.sub.3 0.2 0.2 0.2 0.2 0.2 0.2 CaO + SrO + 10.5 9.5 9.5 11.2 9.5
8.0 BaO + ZrO.sub.2 strain point 578 585 589 558 573 589 (.degree.
C.) volume 11.3 11.2 10.7 11.2 11.2 10.6 resistivity log .rho.
(.OMEGA. .multidot. cm) crack 1030 1500 880 730 2100 1500
resistance (mN) coefficient 85 84 71 80 81 79 of thermal expansion
[30-380.degree. C.] (.times.10.sup.-7/.degree- . C.) density
(g/cm.sup.3) 2.55 2.53 2.49 2.54 2.54 2.55
[0062]
2 TABLE 2 Examples No. 7 No. 8 No. 9 No. 10 No. 11 No. 12
Composition (mass %) SiO.sub.2 68.3 67.2 67.2 62.6 57.1 73.0
Al.sub.2O.sub.3 2.1 2.8 7.2 7.9 7.0 2.0 MgO 3.8 4.5 1.9 3.6 1.5 4.0
CaO 5.0 6.3 7.6 7.5 2.0 7.0 SrO -- -- -- -- 7.0 -- BaO -- 3.1 -- --
8.5 -- Li.sub.2O 1.0 -- 1.0 0.5 -- -- Na.sub.2O 3.6 4.9 2.0 1.9 4.5
13.0 K.sub.2O 10.0 7.9 12.3 12.8 7.5 1.0 ZrO.sub.2 6.0 2.1 0.6 1.9
4.5 -- TiO.sub.2 -- -- -- -- -- -- P.sub.2O.sub.5 -- 1.0 -- 1.1 --
-- SO.sub.3 0.2 0.2 0.2 0.2 0.2 -- CaO + SrO + 11.0 11.5 8.2 9.4
22.0 7.0 BaO + ZrO.sub.2 strain point 533 558 535 578 587 500
(.degree. C.) volume 12.0 11.3 12.0 11.4 11.9 8.5 resistivity log
.rho. (.OMEGA. .multidot. cm) crack 680 700 880 1030 490 880
resistance (mN) coefficient 79 81 84 83 82 89 of thermal expansion
[30-380.degree. C.] (.times.10.sup.-7/.degree. C.) density
(g/cm.sup.3) 2.54 2.54 2.47 2.51 2.80 2.50
[0063] Each of the samples Nos. 1-11 in Tables was produced in the
following manner.
[0064] A glass material batch was prepared to have each glass
composition in Tables, melted in a platinum pot at 1550.degree. C.
for 5 hours, and then poured out onto a carbon plate. Thus, a glass
substrate was produced.
[0065] Each sample thus obtained was evaluated for various
characteristics. The result is shown in Tables.
[0066] As is obvious from Tables, each of the samples Nos. 1-10 as
examples of this invention has a strain point not lower than
533.degree. C., a volume resistivity not lower than 10.6, and a
coefficient of thermal expansion of 71-85.times.10.sup.-7/.degree.
C. and is thus suitable as a rear substrate of an inorganic EL
display. In addition, since the density is not higher than 2.55
g/cm.sup.-3, the weight can be reduced. Furthermore, since each of
these samples has a crack resistance as high as 680 mN or more, it
is assumed that cracks will hardly occur in a production
process.
[0067] On the other hand, the sample No. 11 as a comparative
example has a crack resistance as low as 490 mN. It is therefore
assumed that cracks will easily occur in a production process.
[0068] The sample No. 12 has a low strain point. Therefore, if it
is used as a rear substrate of an inorganic EL display and fired at
650-700.degree. C., thermal deformation will occur. Since the
volume resistivity is as low as 8.5, it is anticipated that the
electric resistance of the electrode material will unfavorably be
changed.
[0069] The strain point in Tables was measured according to ASTM
C336-71. The volume resistivity was measured according to ASTM
C657-78 as a value at 150.degree. C.
[0070] For the crack-resistant characteristic, use was made of a
method proposed by Wada et al (M. Wada et al, Proc., the Xth ICG,
vol. 11, Ceram. Soc., Japan, Kyoto, 1974, p.39). In this method, a
sample glass is placed on a stage of a Vickers hardness tester. A
square pyramid diamond indenter was pressed against the surface of
the sample glass for 15 seconds under various loads. Then, the
number of cracks produced from four indentation corners within 15
seconds after the removal of the load is counted. As a crack
occurrence ratio, the ratio with respect to the number of maximum
possible occurrences of cracks (four) is calculated and the ratio
with respect to the number of maximum possible occurrences of
cracks (four) is calculated. The load when the crack occurrence
ratio is equal to 50% is taken as a "crack resistance". The crack
resistance being great means that cracks hardly occur even under a
high load, i.e., the crack-resistant characteristic is excellent.
The measurement of the crack occurrence ratio was carried out 20
times under the same load and the average was calculated. The
measurement was carried out under the conditions of the temperature
of 25.degree. C. and the humidity of 30%.
[0071] The coefficient of thermal expansion was measured by the use
of a dilatometer as an average coefficient of thermal expansion
within a range of 30-380.degree. C. The density was measured by the
known Archimedes method.
[0072] As described above, the inorganic EL display glass substrate
of this invention has a high strain point not lower than
520.degree. C. as well as a high volume resistivity and a high
crack resistance and is therefore suitable as the rear substrate of
the inorganic EL display.
[0073] The inorganic EL display glass substrate of this invention
has a low density and therefore can be reduced in weight. In
addition, since a large-sized substrate can easily be produced, it
is possible to produce a large-sized home television of 40-inch to
60-inch models. If it is used in a small-sized display, the
productivity is considerably improved.
[0074] Furthermore, if the inorganic EL display glass substrate of
this invention has a coefficient of thermal expansion of
50-100.times.10.sup.-7/.degree. C. within a temperature range of
30-380.degree. C., thermal stress is hardly produced between the
glass substrate and the front substrate or the dielectric
material.
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